Like it or not, uncertainty and climate change go hand in hand

October 25, 2007

Despite decades of ever more-exacting science projecting Earth's warming climate, there remains large uncertainty about just how much warming will actually occur.

Two University of Washington scientists believe the uncertainty remains so high because the climate system itself is very sensitive to a variety of factors, such as increased greenhouse gases or a higher concentration of atmospheric particles that reflect sunlight back into space.

In essence, the scientists found that the more likely it is that conditions will cause climate to warm, the more uncertainty exists about how much warming there will be.

"Uncertainty and sensitivity have to go hand in hand. They're inextricable," said Gerard Roe, a UW associate professor of Earth and space sciences. "We're used to systems in which reducing the uncertainty in the physics means reducing the uncertainty in the response by about the same proportion. But that's not how climate change works."

Roe and Marcia Baker, a UW professor emeritus of Earth and space sciences and of atmospheric sciences, have devised and tested a theory they believe can help climate modelers and observers understand the range of probabilities from various factors, or feedbacks, involved in climate change. The theory is contained in a paper published in the Oct. 26 edition of Science.

In political polling, as the same questions are asked of more and more people the uncertainty, expressed as margin of error, declines substantially and the poll becomes a clearer snapshot of public opinion at that time. But it turns out that with climate, additional research does not substantially reduce the uncertainty.

The equation devised by Roe and Baker helps modelers understand built-in uncertainties so that the researchers can get meaningful results after running a climate model just a few times, rather than having to run it several thousand times and adjust various climate factors each time.

"It's a yardstick against which one can test climate models," Roe said.

Scientists have projected that simply doubling carbon dioxide in the atmosphere from pre-Industrial Revolution levels would increase global mean temperature by about 2.2 degrees Fahrenheit. However, that projection does not take into account climate feedbacks -- physical processes in the climate system that amplify or subdue the response. Those feedbacks would raise temperature even more, as much as another 5 degrees F according to the most likely projection. One example of a feedback is that a warmer atmosphere holds more water vapor, which in itself is a greenhouse gas. The increased water vapor then amplifies the effect on temperature caused by the original increase in carbon dioxide.

"Sensitivity to carbon dioxide concentration is just one measure of climate change, but it is the standard measure," Roe said.

Before the Industrial Revolution began in the late 1700s, atmospheric carbon dioxide was at a concentration of about 280 parts per million. Today it is about 380 parts per million and estimates are that it will reach 560 to 1,000 parts per million by the end of the century.

The question is what all that added carbon dioxide will do to the planet's temperature. The new equation can help provide an answer, since it links the probability of warming with uncertainty about the physical processes that affect how much warming will occur, Roe said.

"The kicker is that small uncertainties in the physical processes are amplified into large uncertainties in the climate response, and there is nothing we can do about that," he said.

While the new equation will help scientists quickly see the most likely impacts, it also shows that far more extreme temperature changes -- perhaps 15 degrees or more in the global mean -- are possible, though not probable. That same result also was reported in previous studies that used thousands of computer simulations, and the new equation shows the extreme possibilities are fundamental to the nature of the climate system.

Much will depend on what happens to emissions of carbon dioxide and other greenhouse gases in the future. Since they can remain in the atmosphere for decades, even a slight decrease in emissions is unlikely to do more than stabilize overall concentrations, Roe said.

"If all we do is stabilize concentrations, then we will still be risking the highest temperature change shown in the models," he said.

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3 comments

UK court says Gore is a fraud. August 2007 Update: Man-made Catastrophic Global Warming Not True. Further, flawed NASA Global Warming data paid for by George Soros. In order to be an intelligent reader you must have a basic knowledge. Please do your own homework; a starting point http://www.InteliOrg.com/

I've always wondered... why are some people so intent on proving that global warming isn't happening/isn't caused by us?

Just assume that they are actually correct (as unlikely as that is). So what? Look around you and you can see people everywhere beginning to care about the environment, governments using less coal and just generally cutting their greenhouse emissions. Would that have happened if everyone was convinced that it isn't caused by us? (because surely everyone knows by now that it IS happening)

But of course we are, at the very least, a contributing factor. So besides making arguments that would stop the population from being environmentally conscious if they were correct, they are also in fact just plainly wrong. The climate change skeptics fail on two accounts, why do they continue?

If you can be bothered to look at the available scientific reports from both sides of the argument you will see that most of any global warming there may be can not be caused by Man.
The Arctic has warmed while the Antarctic has cooled,so any warming there may be isn't strictly global.
The average global temperature has not gone up since 1999(NASA figures)
All that is happening now has also happened in the recent past(alot of it even in the last 100 years or so)with no lasting ill effects.
The IPCC is mostly funded by the UK Government and now the poorer people in Britain are being (green)taxed into abject poverty.
The oil companies are not funding sceptics,they are all for this crap,it pushes oil prices UP!
No matter who is right or wrong,oil will still be used in the future,it's just that the poor in the world not be able to afford it,or even electricity(power prices have increased in the UK because of the carbon credit scam)

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